Technical Field
This disclosure relates to a fixing device and an image forming apparatus incorporating the fixing device.
Related Art
A various types of image forming apparatuses, which employ an electrophotography technique, such as a copier, facsimile machine, and printer, include a fixing device to fix a toner image formed on a recording medium such as a paper sheet to the recording medium. Such a fixing device includes, for example, a fixing roller and a pressure roller. The fixing roller functions as a heating target member to be heated by a heater. The pressure roller functions as a pressing member to be pressed to the fixing roller by a biasing member such as a pressure spring. The fixing roller and the pressure roller form a fixing nip region.
For example, a known fixing device includes a cam, a motor, and a drive transmission mechanism. The cam functions as a moving member to move the pressure roller in a direction to separate from the fixing roller against a biasing force applied by the biasing member. The motor functions as a drive source. The drive transmission mechanism transmits a driving force of the motor to the cam. For example, after completion of image formation, the motor is driven to cause the cam to move the pressure roller from the fixing roller against the biasing force of the biasing member. Therefore, the pressure roller is separated from the fixing roller.
When the pressure roller is moved in the direction to be separated from the fixing roller against the biasing force of the biasing member, a large load torque is applied to the cam. Therefore, in order to drive and rotate the cam, it is expected that the motor has a large drive torque. A motor having a large drive torque is large in size and expensive, which is likely to cause an increase in size and cost of the fixing device and the image forming apparatus incorporating the fixing device.